Certain types of high speed memory circuits may require a reference voltage which provides a level by which the volatile memory and external devices may communicate reliably at high speeds. Maintaining a proper reference voltage to such memory circuits is important for correct operation. In conventional systems, a single reference voltage source is used throughout the operation of the system employing the memory circuits, and consistency of the reference voltage is maintained through use of a single source. However, such systems are inflexible. There is a need for reference voltage sources that may adapt to changing system operating conditions, such as loss of system power.